This invention relates generally to direct contact gas-to-liquid heat exchanger systems and, more particularly, to an induced draft, submerged, horizontal combustion burner water heater and a method of recovering heat from the combustion gas discharged from a submerged burner.
Althouth the present invention can be used in association with a wide range of gas-to-liquid heating devices, it is particularly well suited for use in conjunction with heating domestic hot water. The prior art direct contact gas-to-liquid heating devices were generally vertical burner sumberged combustion devices. These sumberged combustion devices had the combustion source within a can, and the can was submerged in water, Generally, the can was perforated with holes near the bottom to allow flue gas from the burned fuel in the combustion chamber to bubble up through the liquid medium, thereby giving up a portion of its heat to the liquid. However, with the prior art vertical burners there is a tendency for the liquid to sump back through the burner can and flood the burner when the heater is shut off. This is especially true when the heater is required to periodically cycle on and off, such as in domestic hot water heating systems.
In prior art vertical burner submerged combustion systems the burner unit is generally used in conjunction with pressurized air which displaces the water out of the perforated can and into the water tank. The available heat in the flue gas is transferred from the flue gas bubbles directly to the water in the tank. The flue gas bubbles are then exhausted at the top of the water tank while the heated water flows out the water outlet.